The general goal of this project is to further our understanding of the basic mechanisms of cell polarity establishment. The formation of asymmetry within a single cell is fundamental for many different cellular processes, including the development of an organized multicellular organism from a zygote, directional transport of molecules across an epithelial cell layer, motility of a fibroblast cell and the transmission of a nerve impulse. Understanding basic mechanisms of polarity will provide the necessary background for studies of cellular processes important for humans and for studies of many organisms that impact humans both positively and negatively. The brown alga, Pelvetia compressa, provides several advantages for studies of polarity, the most important being the ability to manipulate the developmental axis of the zygote in vivo and therefore to study the process of axis establishment from its inception. These zygotes are naturally responsive to environmental cues, such as unidirectional light, and establish their development axes such that polar growth invariantly occurs from their shaded hemispheres.